Recently, as uses of L-carbohydrate and its nucleoside derivatives are greatly increased in a medical field, a modified nucleoside exhibits a significant potential as a useful anti-virus agent. L-xylulose is a core pentose which constitutes a framework in synthesizing L-ribonucleoside, L-oligoribonucleoside and many agents for use in the treatment. Since L-nucleoside has a high stability from an attack of nucleases, and the like, in a body, when comparing it with D-nucleoside, it is a high potential candidate material which can be used as a material for use in the treatment. Since L-ribose is recently more focused as it is known to have a high usefulness as a raw material for preparing a medicine such as an anti-virus agent, anti-cancer agent, and the like, it is needed to establish a high efficient biological method for preparing L-xylulose.
Despite the above importance and usefulness, xylose and xylulose produced from hydrolysis of plant materials have disadvantages such as a high price, a high production cost, and the like. The hydrolysis treatment of the plant materials results in a low yield and low purity, the acid and material used in the hydrolysis have to be removed by an ion exchange treatment after the hydrolysis treatment, and requires a further purification to be suitable for a food. Such ion exchange and crystalization treatments lead to an increase of the production cost. Therefore, a method for biochemically producing L-xylulose from L-arabitol by using a microorganism and its enzyme has been attemped (Suzuki, T., Tran, L. H., Yoqo, M., Idota, O., Kitamoto, N., Kawai, K., Takamizawa, K. (2005) J. Biosci. Bioeng. 100 (4), 472-474), it is expected that the enzymatic production method for producing L-xylulose by using biocatalysts can overcome the disadvantages. Unlike D-xylulose, since L-xylulose is present in a little amount in the nature, and also has low enzyme stability and enzyme activity, it is difficult to industrialize it (Sullivan, R., Zhao, H. (2007) Appl. Microbiol. Biotechnol., 77, 845-852). Therefore, the enzymatic production method for producing L-xylulose using biocatalysts should secure the enzyme stability and the high enzyme activity.